An optoelectronic device converting optic energy into electric energy vice versa is very important in the electronic information industry nowadays. Such semiconductive optoelectronic devices can be classified into an electroluminescent device, a semiconductive laser device, a light-receiving type device, etc. A flat panel display means generally a device that solves a difficulty of the picture processing by the conventional CRT mode, and a device that has a possibility of expressing at least the same level as that of the CRT mode. The earlier display was mostly used for a hang-on-the-wall television. It has been developing to be applied to a computer monitor, a notebook PC, a PDA terminal, etc. Most of the display means are light-receiving type, whereas an electroluminescent display is magnetic-light-emitting type. The EL display has advantages of a fast responsivity, obviation of a backlight, an excellent luminance as well as a wide viewing angle, so that many applications have been studying in many ways. In case of the EL device prepared from an inorganic material, as the driving voltage is over 220V and the preparation of the EL device is carried out by means of a vacuum deposition, a large size device cannot be prepared and the cost of preparation is very high. However, Eastmann Kodak Company presented a device prepared with a pigment having .pi.-conjugated structure, called "tris(8-hydroxyquinoline) aluminum: Alq.sub.3," in 1987 and thereafter the researches of EL devices using organic material have actively studied. In case of using an organic material, a mechanism of synthesis is simple, it is easy to synthesize materials in the various forms, and color tuning is available, whereas it has disadvantages of low mechanical strength and crystallization caused by heat. To overcome the above disadvantages, an organic EL device having a polymer structure has been researching. In the .pi.-conjugated polymer, a conduction band and a valence band in the energy level are separated by the overlap of .pi.-electron wave function which exists in polymer main chain, a semiconductive property of polymer is decided by a band gap energy which is the energy difference, and a processing of full color is possible. Poly(ethylene terephthalate) had been reported to show electroluminescence in a high electric field. Then, the luminescent device made from poly(p-phenylene vinylene) (hereinafter, "PPV") had been presented, and thereafter it has been studied to apply .pi.-conjugated polymer to an electroluminescent display. The representative organic EL polymer is poly(p-phenylene vinylene)(PPV), which is .pi.-conjugated polymer derivative. Poly(p-phenylene vinylene) derivative used for polymer electroluminescent devices has a drawback of mass production due to poor solubility in an organic solvent, long polymerization time and low polymerization yield.
In general, an organic EL material of PPV has disadvantages as follows:
1) polysulfonium precursor, which is a precursor of PPV, has disadvantages of long polymerization time, low polymerization yield and high cost of preparation; PA1 2) it is difficult to perfectly remove the sulfonium salt; PA1 3) in case of forming a thin film (600 .ANG.), a pin-hole is formed by removing unreacted sulfonium salt, thereby the homogeneity of the film being bad; and PA1 4) it is difficult to synthesize a soluble PPV because of hard conditions of synthesis and polymerization.
The EL devices are classified into a single layer device and a multilayer device. The single layer device has a simple structure having only one polymer layer, and is prepared by a simple process with a low cost. In order to obtain a high efficiency in a single layer device, it is necessary to optimize the transporting balance of carriers such as holes or electrons. In a multilayer device, a hole transporting layer and an electron transporting layer are layer-built. In a single layer device, the EL polymer layer should be able to carry both of holes and electrons. To fabricate a polymer layer of the most ideal single layer device, there is a method of forming a polymer layer which is prepared from a single polymer carrying both holes and electrons. In other ways, there is a method of forming a polymer layer which is prepared by blending two polymers having both of characteristics above, or a polymer layer prepared from a moleculary dispersed polymer in which a specific molecular is dispersed. In other words, a polymer blend of a hole transporting polymer and an electron transporting polymer may be used, and a moleculary dispersed polymer in which carrier transporting molecules are dispersed may be used.
The next generation single layer type device is a device that utilizes a luminescent polymer in which a lower molecular compound having a property of electron transporting and a lower molecular compound having a property of hole transporting are dispersed in the polymer matrix. It is preferred that the polymer matrix is an inert polymer electrically or optically, or a polymer having a property of transporting carriers. But, in case of dispersing lower molecular compounds in the polymer matrix, the lower molecular compounds aggregate upon increasing the temperature, and the device can be deteriorated.
The organic EL polymers of the present invention relates to polymers that can solve the shortcomings of the conventional poly(p-phenylene vinylene) (PPV).